Electromedical implants such as cardiac pacemakers and defibrillators have proven to be an extraordinarily successful instrument for the electrotherapy of bradycardiac and tachycardiac rhythm disturbances. In that respect the task of implants of that kind is not restricted just to merely delivering electrical pulses to the atrium or ventricle myocardium in order there to trigger off depolarization. Rather, modern pacemakers and defibrillators involve sensors and evaluation circuits which permit controlled or regulated frequency adaptation, adaptation of pulse amplitude, pulse width and AV-time for therapy optimization purposes. In that way the aim is for the cardiovascular system of the patient to be modeled as closely as possible on the natural regulating mechanism, in terms of its reaction to physical or psychic loading (frequency- or rate-adaptive cardiac pacemaker).
Electromedical implants at the present time involve a modular design for achieving that aim. Such an implant generally includes elements such as a central control logic, a sensor arrangement for detecting body functions and for intracardial signal recording in the myocardium of the right atrium or ventricle, electrodes anchored in the myocardium, including a circuit for regulating pulse delivery, an energy source for the operating voltage, and a clock and timer unit. It will be appreciated that the specified individual components can be adapted variably to a high degree in respect of their design configuration to the respective conditions prevailing. Therefore the individual components and the appropriate combinations thereof will not be described in detail here as they are known.
Just for reasons relating to circuitry engineering it has been found appropriate for the functions of the implant to be limited to control of the pulse delivery and intracardial signal recording. More extensive tasks such as for example monitoring and optimizing the control itself can generally only be implemented to a very limited degree. That is not only due to the fact that the implementation of such complex control circuits in the limited structural space of the implant encounters at the present time the viable limits thereof. Rather, such a complex control circuit would also result in a markedly increased level of energy consumption so that the service life of the implant would be curtailed. Also, in general a defective control logic system cannot check and re-set itself. For those reasons it has been found appropriate for the electromedical implant and also an external programming device each to be provided with a transmitter and receiver. The telemetry units of the two components provides for the execution of bidirectional data exchange which includes stimulation and diagnostic parameters or recorded intracardial signal and operating parameters respectively.
U.S. Pat. No. 4,705,043 to Imran shows by way of example such an external programming device which provides for evaluation of the transmitted intracardial signals and communicates stimulation parameters to the implant. A disadvantage here is that the external electrical stimulator is an essential part of the control of the implant and, in the event of failure thereof, the implant can continue to operate at best in a predetermined basic configuration.
DE 37 22 829 C2 describes a method in which an implantable electromedical device can communicate with an external programming device, with the transmission of encoded signals. The external programming device generally comes temporarily into contact with the implant, in which case the operating mode and parameters which determine pulse triggering are communicated to an internal programming part of the implant or modified. In that arrangement the external programming device is so designed that it does not communicate with the implant independently but rather only after a given task has been predetermined for it by the programmer (generally the doctor). In practice such programming devices are correspondingly simplified in respect of their technical structure. They essentially consist of the transmitting and receiving unit and numerous interfaces, by way of which peripheral units can be connected. There is no provision for autarchical control. Accordingly the patient has to stay in the clinic in the procedure involving programming, optimization and implementation of an exercise stress test, in which respect he is additionally impeded by extensive cabling. As is known, the unusual surroundings result in what is referred to as the white coat effect in which the cardiovascular system of the patient is precisely not subject to everyday conditions and thus optimization of the stimulation effect is made difficult or entirely prevented.